Geographical distribution of Cacao swollen shoot virus molecular variability in Ghana

Abstract

Cacao (Theobroma cacao L.) was introduced into West Africa from South America during the nineteenth century. However, cacao swollen shoot disease (CSSD) was first observed in Ghana in 1936 and, later, discovered in Nigeria, Côte d’Ivoire, Togo, and Sierra Leone. The objectives of this work were to assess the genetic diversity and spatial distribution of the Cacao swollen shoot virus (CSSV) in Ghana and investigate the origin and spread of the virus by identifying alternative host plants. Results obtained from polymerase chain reaction amplifications and phylogenetic relationship analyses of infected cacao and alternative host plants collected from the cacao- growing regions in Ghana revealed the existence of nine CSSV groups, A, B, C, E, G, J, K, L and M, with six groups detected for the first time in Ghana. The CSSV groups in Ghana are very divergent and correspond to at least five different putative species, according to the International Committee on Taxonomy of Viruses recommendations (A, B-C complex, G, E, and M), with the M species only being detected in the alternate host Ceiba pentandra. The spatial distribution of the different molecular groups in Togo, Côte d’Ivoire, and Ghana makes it difficult to predict a single origin for CSSV among the West African cacao-growing countries.